The present invention relates to a slide valve. One aspect relates to a slide valve as combined with components of a liquid reaction--or liquid injection--molding system. An aspect relates to a slide valve having a spool valve element and modus operandi featuring unidirectional spool movement, precompression of the fluid being controlled, and excess pressure relief means. The slide valve of the present invention is described with reference to a liquid reaction molding system.
Liquid reaction molding (LRM) and systems for practicing same are described, inter alia, in U.S. Pat. Nos. 3,908,862; 4,008,829; and 3,912,234. Very briefly LRM comprehends thoroughly mixing two liquid reagents that will react to form a solid plastic body and then, before it solidifies, injecting the mixture into a mold where it does solidify. Its advantages compared with conventional plastic injection molding include lower molding pressure, less energy required for molding, ready adaptability to large (e.g. automative body parts size) parts molding, and acceptably high production rates and quality (again, e.g., automotive body parts). The reagents must be carefully measured and thoroughly mixed to achieve the desired quality and rate of curing (i.e. solidifying) to which ends are directed, e.g., the systems of U.S. Pat. Nos. 3,908,862 and 4,008,829.
The LRM system of the enumerated patents for measuring and mixing of these references use three two-way ball valves and one check valve to accomplish directional flow control of each reagent. There being two reagents (normally), there are six ball valves and two check valves in such systems. The ball valves develop stem leakage problems during service with ordinary reagents. When the reagents contain fillers (which more and more they do in order to improve mechanical properties) such as mineral pigment, fiberglass, or carbon black, acute valve seat wear occurs, especially on the ball valves.
Spool type valves in LRM are known. German Auslegschrift 23 64 501 shows one such in detail. Spool valves in servo control systems with lands, grooves and hollow spools are known, e.g. U.S. Pat. to Vickers No. 1,928,144 and Tyler U.S. Pat. No. 2,655,903. The present invention and systems including it differ structurally and functionally, e.g. in the compression and pressure relief features.
The present invention contemplates a spool type or slide valve one of which replaces the three ball valves and one check valve in an LRM system while reducing the problems of stem leakage and seat wear. The instant spool type valve also provides means to precompress or prepressurize the reagent being controlled and also means to relieve excessive downstream pressure.
The preferred slide valve construction has a hollow spool with one groove between two lands for making and breaking (blocking) flow paths among four serially arranged ports that open into the valve chamber. The valve contemplates unidirectional movement of the spool to make and break fluid flow paths in a desired sequence. One end of the spool is free, the other end is connected to a hydraulic drive piston. One of the ports is at the far end of the valve chamber, where it is in constant full communication with the free end of the spool and the spool interior, which is the structure feature that achieves, both the precompression and relief features.
More specifically the invention embraces a reciprocating slide valve having a spool valve member that is slidably movable in one direction to or through three positions (first, intermediate; and injection, respectively) and comprising an elongated body having therein a bore constituting a valve chamber and a hollow spool valve slidably mounted in the bore. Drive means to unidirectionally move and position the spool valve at each of said positions in sequence. The body has first, second, third, and fourth valve chamber ports arranged serially in the wall of the chamber and progressing from one end to the other of the chamber. The spool has first and second lands spaced by a groove. The groove and first and second chamber ports are axially located and sized to connect the first and second chamber ports when the spool valve is in intermediate position and for the groove to be in communication with at least the second chamber port when said spool valve is in injection position. The spool second land establishes a communication path between the third and fourth chamber ports when the spool is in first position and blocks said path in the other two positions. The spool is hollowed by axially extending passage means extending between the lands for establishing communication when said spool valve is positioned at said injection position between the fourth chamber port and a predetermined one of said other chamber ports--normally the first port--but to block the last said communication at the other positions.